<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>

    <script>

        // 0-100之间的随机数
        var n = Math.ceil(Math.random() * (100 - 0) + 0) ;


        // 100
        // 90-99       
        // 80-89
        // 70-79
        // 60-69
        // 0-59


        // 
        n = parseInt(n / 10) ;
        
        document.write(n) ;

        switch(n) {
            case 10 : {
                alert('666') ;
                break ;
            }
            case 9 :  
            case 8 : 
            case 7 : 
            case 6 : {
                alert('及格') ;
                break ;
            }
            default : {
                alert('下个班见') ;
            }
        }

    </script>
    
</body>
</html>